The invention is directed to a method and apparatus for extracting gold from gold ore by comminution, agglomeration and leaching of the ore.
Metallic gold is usually extracted from gold ores by leaching the ore, for example with a cyanide solution, and subsequent recovery from the solution by precipitation or adsorption. Standard methods for leaching are what are referred to as agitator leaching or bulk leaching. A trickle leaching in basins is also occasionally employed. The present invention is directed to the processing of the ore for bulk leaching and can also be employed for basin leaching.
A number of prerequisites are needed so that the lixivium sprinkled on the ore pile can optimally dissolve the gold to a great extent:
1. The ore must be comminuted to such an extent until nearly all elemental gold particles enclosed therein are opened up, i.e. every gold particle must have a part of its surface tangential with the surface of the ore particle. It would also suffice if the ore particle were permeated such as by micro-cracks so that the lixivium can penetrate into the interior of the ore particle and dissolve the elemental gold situated there. This effect, however, cannot occur with a conventional ore comminution. PA1 2. The ore charge must be adequately permeable for the lixivium in and of itself so that the lixivium can reach all ore particles. The permeability within the ore pile must be uniform, otherwise, the lixivium will seek paths of least resistance and a part of the ore will not be leached. For example, having the leach rinse superfine grains from the upper portions of the pile between coarser particles cannot occur, and the superfine grains collecting in the lower region and seal this region like a clay layer. PA1 3. Finally, an adequate volume of air-filled pores is also needed in the ore batch because the cyanidic lixivium requires the presence of oxygen. PA1 (a) conventional comminution to less than 20 mm, rolling granulation after addition of 1% portland cement and 3% water; PA1 (b) inventive comminution and agglomeration following prior addition of 3% water in the high pressure roller press with a relative pressing power of 44 kN per cm of scab width referred to 1 m roller diameter without a bonding agent additive; PA1 (c) inventive comminution and agglomeration in the high-pressure roller press following prior addition of 1% portland cement and 3% water, whereby a relative pressing power of 43 kN per cm of scab width was established.
In order to satisfy these prerequisites, it is standard to first comminute (for example, to less than 20 mm) the ore for the purpose of digestion and to then granulate it upon addition of some bonding agent, for example cement, by means of a rolling ore make-up granulation, usually granulating drums. The required porosity of the charge for lixivium passage and for air access is thus achieved. The superfine grain contained in this crushed ore is also bonded and cannot be rinsed out.
The ore particles, however, are now bonded in the granules. When these are too dense, then the access of the lixivium to the ore particles is made more difficult. When relatively porous granules are produced, the lixivium can in fact penetrate but the strength of the granules is low and there is the risk that the granules will be compressed by the load of the layers situated thereabove, and the porosity of the individual granules as well as the charge as a whole is lost.
Optimum conditions, consequently, can only be achieved with difficulty. Moreover, the overall process for the processing the ore for the subsequent leaching, involves the method steps of comminution, dosing with the bonding agent, mixing and rolling granulation.
It is an object of the invention to obtain a method and apparatus in extracting gold from gold ore comprising comminution and leaching of the ore which will save capital and operating costs, particularly to reduce the costs for the ore grinding without having to accept a decrease in the gold yield.
A further object of the invention is to provide an improved method and apparatus for the extraction of gold from ore particles which obtains an improved and more uniform extraction providing improvements over methods and apparatus heretofore available.
A further object of the invention is to provide a process and apparatus for use in extracting gold from gold ore wherein the ore is initially subjected to interparticle crushing and the ore thereby yields itself to improved treatment by leaching.